The sweat produced by eccrine sweat glands is primarily composed of:

Correct Answer: A

Rationale: Eccrine sweat glands produce sweat mainly of water and electrolytes (e.g., sodium, chloride), secreted to the skin surface for cooling and minor waste excretion. Sebum, an oily lipid mix, is from sebaceous glands. Melanin is a pigment, not in sweat. Blood plasma, while fluid, contains proteins and cells not found in eccrine sweat, which is filtered and simpler. This watery, salty composition enables evaporative cooling, distinguishing eccrine sweat's role in thermoregulation, making it the correct answer.

Correct Answer: B

Rationale: The stratum basale, the deepest epidermal layer, produces new skin cells via mitosis of basal keratinocytes, regenerating the epidermis as cells move up and keratinize. Sensation involves dermal receptors, temperature regulation uses sweat and vessels, and sebum secretion is from dermal glands, not the basale. Its role as the proliferative base, sustaining skin renewal, makes it the correct primary function.

Correct Answer: B

Rationale: Fibroblasts in the dermis produce collagen and extracellular matrix during wound healing, driving repair and regeneration by rebuilding tissue post-injury. Melanocytes make melanin, not repair tissue. Macrophages clear debris and fight infection, aiding but not leading regeneration. Adipocytes store fat, not regenerate skin. Fibroblasts' role in scar formation and dermal restoration is central to skin repair, making them the key cells.

Correct Answer: C

Rationale: Arrector pili muscles generate goosebumps by contracting to raise hairs, a response to cold or emotion, historically for insulation or threat display. Melanin is from melanocytes, 'ejecting hair shafts' misrepresents their action (though they move hairs), and temperature regulation is indirect, primarily vascular/sweat-based. Goosebumps are their hallmark effect, making this the primary function.